linux-kernel - Re: [PATCH V2 11/19] csky: Atomic operations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 7 Jul 2018 22:10:24 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Guo Ren <ren_guo@...ky.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        daniel.lezcano@...aro.org, jason@...edaemon.net, arnd@...db.de,
        c-sky_gcc_upstream@...ky.com, gnu-csky@...tor.com,
        thomas.petazzoni@...tlin.com, wbx@...ibc-ng.org,
        green.hu@...il.com, Will Deacon <will.deacon@....com>
Subject: Re: [PATCH V2 11/19] csky: Atomic operations

On Sat, Jul 07, 2018 at 04:08:47PM +0800, Guo Ren wrote:
> On Fri, Jul 06, 2018 at 02:17:16PM +0200, Peter Zijlstra wrote:

> 	CPU0			CPU1
> 
> 	WRITE_ONCE(x, 1)	WRITE_ONCE(y, 1)
> 	r0 = xchg(&y, 2)	r1 = xchg(&x, 2)
> 
> must not allow: r0==0 && r1==0
> So we must add a smp_mb between WRITE_ONCE() and xchg(), right?

The state (r0==0 && r1==0) _must_ not be allowed in the above snippet (so,
even without the additional smp_mb() between WRITE_ONCE() and xchg()).  In
informal terms, xchg() provides the smp_mb().

Compare implementations of xchg() and xchg_relaxed().  The following could
also be helpful (in addition to the references pointed out earlier):

  Documentation/atomic_t.txt

  Andrea


> 
>  Guo Ren
>